Characterization of GPS-TEC in a low-latitude region over Thailand during 2010-2012

Abstract

This paper presents the first results of vertical total electron content (VTEC) data from (1) a dual-frequency GPS receiver installed at the Chiang Mai University in Chiang Mai (CHGM, 18.480 N, 98.570 E) as part of SCINDA (Scintillation Network and Decision Aid) and (2) the International GNSS Service (IGS) station Pathum Wan (CUSV, 13.735 N, 100.533 E) with magnetic latitude of 8.69°N and 3.92°N respectively in Thailand, from August 2010 to July 2012. In the equatorial ionization anomaly (EIA) region, these two stations are separated at a distance of 668 km. Observed GPS-TEC values were found to be the highest between 1500 and 1900 Local Time (LT) throughout the study period at both the stations. The GPS-TEC data from both the stations was plotted diurnal, monthly and seasonal analyses were performed. The equinox (March, April, September, and October) and solstice (January, February, June, July, and December) periods had maximum and minimum diurnal peak variations, respectively, of the GPS-TEC. High TEC values are attributed to extreme solar ultra-violet ionization coupled with upward vertical E×B drift. A comparison of the GPS-TEC data from both the stations for the study period shows that the CHGM station recorded higher values of TEC than the CUSV station because of the formation of an ionization crest over the CHGM station. The GPS-TEC values also exhibited an increasing trend-because of the approach of solar cycle 24. For data validation, the diurnal, monthly, and seasonal variations in the measured TEC were compared with the TEC modelled in the International Reference Ionosphere (IRI) models (IRI-2007 and the recently released IRI-2012 model). The IRI-2007 shows good agreement with the data from 2010 to 2011 from both stations and IRI-2012 agrees well with the data from 2012 onwards compared to IRI-2007.